1. Field of the Invention
This invention relates to a novel composition for use in dental flosses or tapes. More particularly, it relates to novel compositions containing a base polymer, a block copolymer and a nonmigrating compatibilizer or plasticizer that, in combination in a blend, result in a floss or dental tape having good breaking strength, tenacity, nick resistance and elongation properties. It also relates to a novel extruded, flattened, monofilament tube structure useful in dental tapes and flosses, as well as a method for making such structure. It also relates to a flattened monofilanent tube that is textured along the longitudinal axis as well as perpendicular to this axis.
2. Prior Art
The use of polymer compositions in dental flosses and tapes has been known previously. However, there have been continuous efforts to develop a floss which does not shred or fray upon use and which has sufficient tensile strength for use between the teeth.
For example, U.S. Pat. No. 2,381,142 (Stonehill) describes a dental floss made from a strand or filament of synthetic fibers of an unplasticized vinyl resin such as a copolymer of vinyl chloride and vinyl acetate treated with wax.
U.S. Pat. No. 3,359,344 (Fukushima) describes a method for manufacturing a spun fiber. According to Fukushima, a polymer selected from the group of polyethylene, polypropylene and polystyrene having a melting point lower than 170xc2x0 C. is mixed with a second polymer selected from polyamides and polyesters having a melting point greater than 170xc2x0 C. and an additional amount of the first polymer. The composition is blended and extruded to form a fiber.
In U.S. Pat. No. 3,639,505 (Hughes et al.), there is described a method of improving the dyeability of polyolefin fibers and films. The method includes forming a polymer alloy containing a blend of polyolefin, a minor amount of polyethylene terephthalate and from 0.2 to 5 parts per hundred parts of polymer of toluenesulfonamide compound.
U.S. Pat. No. 3,800,812 (Jaffe) describes a dental floss made from a polyester elastomer, including Hytrel (available from DuPont). The elastomer is extruded into a hot and tacky tape, then cooled.
U.S. Pat. No. 3,900,549 (Yamane et al.) describes a method for preparing composite filaments composed of a polyethylene and a polyester. The method includes the steps of mixing a polyethylene having a melt index of above 27 with a polyester having a specific inherent viscosity, the proportion of the polyethylene being 5 to 15% or 25 to 90% based on the total weight of the mixture, melt extruding the resulting mixture through a spinneret and then withdrawing the extruded filaments at a speed of above 2,500 meters per minute.
U.S. Pat. No. 3,957,056 (Ferraro et al.) describes a dental floss containing aromatic polyamide fibers having at least 35% of the amide linkages attached directly to two aromatic rings.
U.S. Pat. No. 4,552,603 (Harris, Jr. et al) describes heat bondable bicomponent fibers containing polyester and another thermoplastic polymer having a melting point which is at least 15% C. below that of polyester.
U.S. Pat. No. 4,583,564 (Finkelstein et al.) describes a dental floss consisting of filaments containing a higher melting point core material and a lower melting point sheath material. The sheath material fibers are fused by subjecting them to a temperature sufficient to fuse them.
U.S. Pat. No. 4,609,710 (Iohara et al.) describes an undrawn polyester yarn and process for manufacturing such yarn. The main acid component of the yarn is an aromatic dicarboxylic acid.
U.S. Pat. No. 4,986,288 (Kent et al.) describes dental floss and toothpicks which contain one or more coagulants to retard and stop bleeding during flossing.
U.S. Pat. No. 4,996,056 (Blass) describes a dental floss or tape containing fluorocarbon polymer powder particles as a solid lubricant.
Despite the existence of such products as described heretofore, there still exists a need for dental floss and tape products having high breaking strength, high tenacity, nick resistance and suppleness which does not fray or break easily when used. Furthermore, there is a need to have dental floss or tape which is gentle to gum tissue which can be manufactured at high speed and low cost.
It is, therefore, an object of this invention to provide an extruded, flattened, monofilament tube with rounded edges suitable for use as a dental floss or tape.
It is another object of this invention to provide a flattened, monofilament tube that is textured along the longitudinal axis as well as perpendicular to this axis.
It is another object of this invention to provide a polymer blend resulting in an acceptable dental floss or tape.
It is another object of this invention to provide a dental floss or tape having high breaking strength, high tenacity, nick resistance and suppleness which does not fray or break in use.
Another object of this invention is to provide a method for making a polymer blend resulting in an excellent composition for use in dental flosses and tapes.
Another object of this invention is to provide a method of making polymer blend products in the form of a monofilament for use as a dental tape or floss.
Yet another object of this invention is to provide low cost, high grade polymer compositions for use in dental flosses and tapes.
Additional objects will become apparent throughout the ensuing description of the products and processes of this invention.
This invention relates to novel compositions useful in making dental flosses and tapes. The compositions of this invention are extrudable and can be formed into a monofilament.
Dental flosses and tapes made with the novel compositions of this invention may be formed into an extruded, flattened, monofilament tube with rounded edges. The unique monofilament shape provides rounded edges that will not cut or irritate gingiva tissue. The composition allows the monofilament to meet two primary concerns of the dental floss consumer: ease of passage between teeth and resistance to fraying. The composition provides a supple, slippery material that is capable of sliding and compressing as it moves between teeth. The individual fiber composing the novel monofilament structure and composition does not break and is not perceived to fray as do ordinary dental flosses, which are composed of many fine monofilaments. It has been found that, upon preparation for use, the user generally stretches the floss or tape prior to insertion between the teeth. We have discovered that the flosses of this invention elongates and reduces its thickness such that it easily slides between the teeth. The monofilaments of this invention can elongate at least about 30% of their original length and can reduce their thicknesses at least about 10%.
The flosses of this invention can be textured along the longitudinal axis as well as perpendicular to this axis. This textured floss, which still slides easily between the teeth due to its unique composition, enhances the floss"" effectiveness by exerting gentle pressure interstitially.
More particularly, the products of this invention relate to novel compositions containing a base polymer, such as a polyolefins, modified polyamides, polyesters or polyurethanes; block, or segmented, copolymers such as modified polyamides, polyesters or polyurethanes; and nonmigrating compatibilizer(s) or plasticizer(s) that in combination result in a polymer blend which can be formed into a monofilament having good breaking strength, tenacity, nick resistance and elongation properties.
The products of this invention are considered, generally, xe2x80x9cpolymer blendsxe2x80x9d. Polymer blend technology involves the mixture of different polymers, and has been necessitated by the increasing costs of synthesizing new polymer structures. It has been discovered that certain polymer blends, surprisingly, exhibit novel, unusual and unexpected properties different from the constituent polymers. The blending of polymers with careful control of the resulting blend""s morphology by consideration of the rheological and thermodynamic properties of the individual components have led to new polymer blends of commercial interest.
The compositions of this invention generally have three constituent components: a base polymer, a block copolymer and a compatibilizer. The base polymer, which is selected from the group of polyolefins, modified polyamides, polyesters or polyurethanes, provides strength and tenacity; it may also impart suppleness. The segmented or block copolymer component assists in providing nick resistance and elasticity. In general, many polymer pairs are thermodynamically incompatible. In order to facilitate intimate polymer blending, a polymeric compatibilizer should be introduced into the compositions of this invention. The compatibilizer acts as a molecular bridge between the polymers, similar to the action of a surfactant in emulsifying oil and water systems. Thus, the nonmigrating compatibilizer assists in providing integrity to the composition. This, in turn, contributes to the suppleness of the compositions and assists in melt processing and post-extrusion drawing of the monofilament tube by reducing melt viscosity and improving elongation characteristics.
The compositions of this invention are used in making flosses and tapes having excellent attributes. In use, dental flosses and tapes must have a high breaking strength, high tenacity and a suitable denier and thickness. They should also have a softness or suppleness such that they can easily be handled by the consumer. In practice, the dental floss or tape must not easily nick and break when the consumer encounters a sharp edge in flossing teeth and must not elongate too readily. The polymer blends of this invention have all of these attributes. In addition, they are capable of being pigmented, readily processible on extruders using tubular die or spinneret die technology and may be waxed to accept flavors.
The products of this invention may be made by blending all the individual polymers in pellet or powder form in a dry mixer. They are then compounded on a twin screw compounding extruder and pelletized. Additionally, the individual polymer pellets may be gravity fed to a twin screw compounder to form the pellets of the compounded polymer blend. The compounded pellets are then extruded in a single screw extruder with a die head having an appropriate tubular or spinneret die. The extruded polymer is drawn down in a highly oriented form, annealed and calendered to achieve an appropriate thickness.